1. Field of the Invention
The present invention relates to a high-strength connection for expandable members, and more particularly, to a threaded flush joint connection for radially expandable tubulars, such as tubulars used in the oil and gas industry.
2. Description of Related Art
In a typical oil or natural gas well drilling environment, a plurality of tubulars, e.g., pipes, are inserted one at a time into a well bore hole in strings of different diameters, thus forming a telescopic well design. The assembly of such pipes used in the oil and gas industry is commonly performed using threaded joints or connections, the standards for which are described and specified by the American Petroleum Institute (“API”). These connections have limitations when subjected to extreme loading conditions, which are increasingly common in today's oil and gas wells. This is especially true with connections used in a high internal or external gas pressure environment, where the risk of leaks must be eliminated, yet the connections must resist high mechanical loading conditions caused by tension or other loads.
One of the newest and most demanding technologies used in oil and gas well drilling today is “expandable technology.” In accordance with this technology, a tubular member, e.g., a pipe, may be radially expanded by means of a mandrel after the pipe has been lowered into a well, which mandrel is moved along the internal diameter of a string of such pipes. Each pipe in the string is enlarged in place to allow other pipes to be lowered and expanded as well, so that ultimately all the pipes in the well have the same internal diameter, thereby avoiding the reduction in internal diameter of the ordinary telescopic well design. Today, such a string of pipes is normally radially expanded by more than five percent, with the industry targeting expansions of greater than twenty percent, based on an internal diameter of the pipe being expanded. One process of expanding tubulars is described in detail in U.S. Pat. No. 5,348,095 to Worrall et al., which is incorporated herein by reference. An alternative expansion method, which utilizes rotary devices, is described in detail in U.S. Pat. No. 6,457,532 to Simpson, which is also incorporated herein by reference. Yet another alternative method of expanding expandable tubulars is described in substantial detail in U.S. Pat. No. 6,604,763 to Cook et al., which is also incorporated herein by reference.
At first, the expandable tubulars or tubular members, e.g., pipes, and the connections to join them were mainly used for casing remediation or similar applications, where the length of the string of pipes was relatively small, thus allowing for low-strength connections. However, with increasing well depths and the consequent increase in the length of the string of pipes, an important design element to be considered is the increased strength of the connection needed. Previous expandable connections, such as the connections in expandable tubular technology utilizing slotted pipes as tubulars, needed only to withstand loads associated with the running and expansion processes. However, as technology for the expansion of solid (i.e., neither slotted nor perforated) tubulars is being spread within the oil and gas industry, another tubular connection design element that should be considered relates to the capability of the connections to assure fluid and/or gas tightness against internal pressure, external pressure, or both.
To provide a high-strength connection between two tubulars, different alternatives have appeared in the oil and gas industry, such as the so-called “upset ends” and “coupling” connections. However, the least problematic radial expansion processes require that the connection and the tubular members have substantially the same wall thicknesses so that the force necessary to deform (i.e., radially expand) the string of pipes is substantially constant as a mandrel, for example, is moved along the pipe string. As such, the connections should preferably be of the type known in at least the oil and gas industry as “flush joint” or “integral flush joint”, in which the connections are threaded within the wall thickness of the tubular member, with a male threaded element at one end of the tubular member and a female threaded element on the other end. The external diameter of such a flush joint connection is the same for both tubular members that are to be “made up,” or threaded together and torqued, to achieve a desired connection and seal. In these flush joint connections, however, any device (e.g., an O-ring) that is placed within the threads or at the ends of the threaded areas of coupled tubular members diminishes the “critical area”, also known as the resistant area. For the female tubular member, this critical area of the connection is the area defined as the circular ring bounded by the external diameter of the connection and the diameter of the thread root of the female member at the last engaged thread of the male member; and for the male tubular member, this critical area is the circular ring bounded by the diameter of the thread root of the male member at the last engaged thread of the female member and the internal diameter of the connection. Therefore, devices placed within the wall thickness, such as O-rings (see, e.g., U.S. Pat. No. 6,409,175 to Evans et al.), will reduce this critical area and consequently the tensile resistance of the threaded connection, which in turn limits the length of the tubular string and the depth that can be achieved therewith as the reduced critical area cannot withstand the required higher loading. As such, a need exists in at least the oil and gas industry for an expandable connection, such as a threaded flush joint connection, having an improved critical area that can withstand today's high loads.
To assure a threaded connection's sealing response, some standard connections in the oil and gas industry rely on metal-to-metal seals placed at various points in the joints depending on the joint design, which points are selected to improve the leak resistance of the connection. This type of seal in a threaded joint provides a barrier to gas or liquid pressure while the threads provide mechanical support and help or even improve stabbing and running characteristics. One example of this type of metal-to-metal seal is the API “Extreme-Line” joint, as defined by API Standard 5B. Several seal design alternatives to metal-to-metal seals have been proposed in the known art. For example, other connections make use of a resilient seal located at a given position along the threaded area, wherein this resilient seal plastically deforms during make up of the connection and the connection obtains sealability as a consequence of the thread gaps being closed by the compression of the resilient material between the mating elements (i.e., within the thread gaps). In another type of connection, small gaps formed between the threads of the mating members of the connection are filled with an API Modified Thread Compound, which is a thread compound that is formulated in accordance with the requirements of obsolete API Bulletin 5A2 (i.e., a grease-based compound). All of these types of sealing mechanisms cannot work properly in an expandable threaded tubular connection after a radial expansion thereof, as there is a tendency for the threads of the female tubular member to shift or separate from the threads of the male tubular member thereby creating leak paths along the connection.
In expandable threaded connections, yet another design aspect that should be considered is the design of the threads. Conventional thread designs for expandable threaded connections have included (i) “perfect threads”, as shown for example in FIG. 15A, which are threads having normal (i.e., perfect) roots and normal (i.e., perfect) crests, such as disclosed in U.S. Patent Application Publication No. 2003/0107217A1 to Daigle et al., and (ii) “hooked threads”, as shown for example in FIG. 15B, such as disclosed in U.S. Pat. No. 6,409,175 to Evans et al. However, a need remains in the oil and gas industry for an expandable threaded connection having strength greater than that obtained with these conventional forms of threading.
Finally, some connections have been developed for use with expandable tubulars, which are disclosed in varying detail in the following patents and patent applications: U.S. Pat. No. 6,409,175 to Evans et al.; European Publication No. 1106778A1; and U.S. Patent Application Publications No. 2002/0163192A1 to Coulon et al., No. 2003/0067166A1 to Sivley, IV, and No. 2003/0107217A1 to Daigle et al.
However, despite the conventional connections described above for radially expandable tubular members, a need remains in the oil and gas well drilling industry for a high strength, yet simple to manufacture and easily made up, expandable threaded connection that remains sealed after a radial expansion thereof and which can sustain the increasing loads being placed on such connections as a result of today's increasingly deeper, higher pressure wells.